<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        function changeDemo() {
            document.getElementById("demo").innerHTML = Date();
        }
    </script>
</head>
<body>
<p id="demo">我要被时间替换你们信吗？不信就演示给你看</p>
<button onclick="changeDemo()">点我，有惊喜</button>
</body>
</html>